1. Field of the Invention
The present invention relates to a radio circuit used for radio communication and the like and a control method of the radio circuit, particularly to reduction of the power consumption of a receiving circuit.
2. Description of the Related Art
A radio circuit requires an ability to receive a desired signal even when an interfering wave is input at a predetermined level range. One of deterioration factors of the receiving characteristic due to an interfering wave is deterioration of the receiving characteristic due to reduction of a gain caused by saturation of a receiving circuit due to an interfering wave at a strong level when the level of the desired signal is low.
FIG. 9 shows a basic configuration of a conventional radio circuit. In FIG. 9, the radio circuit comprises a receiving circuit 101, a transmitting circuit 102, a receiving RF filter 103, a transmitting RF filter 104, an antenna 105, a local oscillator 106, and a base-band circuit 107. Signals having unnecessary frequencies out of signals received by the antenna 105 are reduced or attenuated by the receiving RF filter 103, and then the remaining signals are input to the receiving circuit 101. The receiving circuit 101 selects a signal with a desired frequency from the remaining signals in accordance with the output signal frequency of the local oscillator 106, demodulates the selected signal, and outputs the demodulated signal to the base-band circuit 107.
The transmitting circuit 102 modulates an output signal of the local oscillator 106 in accordance with a modulating signal supplied from the base-band circuit 107 to generate a transmission signal. The transmitting RF filter 104 reduces unnecessary frequency components from the signal transmitted from the transmitting circuit 102. Then, the transmission signal is transmitted from the antenna 105.
In the case of the above conventional radio circuit, power consumption of the receiving circuit 101 is continuously increased to expand the linear operation range in order to prevent the receiving circuit 101 from being saturated due to a strong-level interfering wave. Therefore, there is a problem that a large power consumption is generated even under a state of receiving no interfering wave.
The present invention has a purpose to provide a radio circuit and a control method of a radio circuit, in which a desired receiving characteristic can be achieved even when a strong-level interfering signal is received, but the power consumption of a receiving circuit when no interfering wave is received can be decreased.
In a first aspect of the invention, provided is a radio circuit comprising: a receiving circuit including at least one circuit of which linear-operating range changes in accordance with power consumption, the receiving circuit receiving radio signals and selecting a signal having a desired frequency from the received signals to demodulate the selected signal; an input-power detector for detecting power input to the receiving circuit; a received-power detector for detecting power of the signal selected by the receiving circuit; and a control circuit for controlling the receiving circuit. When the power detected by the input-power detector is larger than a first predetermined value and the power detected by the received-power detector is smaller than a second predetermined value, the control circuit increases power consumption of the circuit which is included in the receiving circuit and of which linear-operating range changes in accordance with power consumption to expand the linear operation range and thereby to make the receiving circuit operate at a low distortion.
In a second aspect of the invention, provided is a radio circuit comprising: a receiving circuit including at least one circuit of which linear-operating range changes in accordance with power consumption, the receiving circuit receiving radio signals and selecting a signal having a desired frequency from the received signals to demodulate the selected signal; an input-power detector for detecting power P1 input to the receiving circuit; a received-power detector for detecting power P2 of the signal selected by the receiving circuit; and a control circuit for controlling the receiving circuit. When the value of the power ratio P2/P1 based on the power P1 detected by the input-power detector and the power P2 detected by the received-power detector is smaller than a predetermined value, the control circuit increases power consumption of the circuit which is included in the receiving circuit and of which linear-operating range changes in accordance with power consumption to expand the linear operation range and thereby to make the receiving circuit operate at a low distortion.
In the radio circuit, the receiving circuit may include a filter for selecting a signal with a specific frequency to be received. The circuit of which linear operation range changes in accordance with the power consumption may be disposed immediately before the filter.
In the radio circuit, the receiving circuit may include a gain adjustment circuit for adjusting a signal gain, and decrease the gain of the gain adjustment circuit when the power detected by a received-power detector is larger than a predetermined value to suppress power consumption of at least one of the gain adjustment circuit and circuits disposed subsequently to the gain adjustment circuit.
In the radio circuit, the receiving circuit may comprise a first path, a second path of which power consumption is large than that of the first path and of which linear operation range is wider than that of the first path, and a switch for selecting either of the first and second paths in accordance with outputs of the input-power detector and the received-power detector. The path which is not selected may be controlled to stop its operation.
In the radio circuit, the second path may include a low-noise amplifier, and the input-power detector may detect the power at a point on the output side of the low-noise amplifier.
In the radio circuit, when the receiving circuit selects and receives a desired signal out of signals in a plurality of frequency bands, any signals in the plurality of frequency bands may be received through the same circuit in the receiving circuit.
In the radio circuit, reception can be performed under transmission.
In a third aspect of the invention, provided is a method of controlling a radio circuit comprising a receiving circuit including at least one circuit of which linear-operating range changes in accordance with power consumption, the receiving circuit receiving radio signals and selecting a signal having a desired frequency from the received signals to demodulate the selected signal. The method comprises: detecting input power being input to the receiving circuit; detecting receiving power of the signal selected by the receiving circuit; and increasing power consumption of the circuit which is included in the receiving circuit and of which linear-operating range changes in accordance with power consumption to expand the linear operation range and thereby to make the receiving circuit operate at a low distortion, when the detected input power is larger than a first predetermined value and the detected receiving power is smaller than a second predetermined value.
In a fourth aspect of the invention, provided is a method of controlling a radio circuit comprising a receiving circuit including at least one circuit of which linear-operating range changes in accordance with power consumption, the receiving circuit receiving radio signals and selecting a signal having a desired frequency from the received signals to demodulate the selected signal. The method comprises: detecting input power being input to the receiving circuit; detecting receiving power of the signal selected by the receiving circuit; and increasing power consumption of the circuit which is included in the receiving circuit and of which linear-operating range changes in accordance with power consumption to expand the linear operation range and thereby to make the receiving circuit operate at a low distortion, when the value of the power ratio P2/P1 based on the detected input power P1 and the detected receiving power P2 is smaller than a predetermined value.